The present invention relates generally to the field of heat exchangers, and more particularly, is directed to a combination heat exchanger and blower which is designed to reduce the lost heat at chimneys.
Prior workers in the field have employed heat exchangers of many types wherein heat from a first source is applied to a second medium. Most frequently, the presently available heat exchangers employ tubes which are surrounded by a heat absorbing medium such as water. Accordingly, when hot gases such as generated by a boiler, are directed through the tubes, the water surrounding the tubes can absorb some of the heat as it passes through the tubes to thereby heat the water, for other use such as feedwater to a boiler. Another type of heat exchanger that is commonly employed relates to an air preheater for use in large boiler plants. In such preheater designs, the flue gases are directed through a row or rows of coils prior to exiting through the stack to heat the combustion air before it enters the boiler. Thus, as the flue gases are directed to the stack, the heat of these gases which would otherwise be wasted is utilized to preheat the combustion air before it enters the boiler. However, it is noteworthy that the prior art types of heat exchangers suitable for use with boilers all relate to large installations and these designs cannot be utilized with small equipment such as a residential size heating unit.
Many similar types of installations are available and have long been utilized in the mechanical art field. However, most prior art heat exchangers are quite inefficient in operation and in function and cannot be designed to make economical use of the available heat, especially when applied to relatively small heaters.
The rate of heat exchange varies with the temperature differential between the heating medium and the liquid to be heated, with the length of time during which heat exchange may take place and with the velocity with which the heated gases are moved over the surface of the coils. It is well known that the rate of heat transfer by convection in a furnace will be considerably modified by the velocity of flow of the furnace gases. A boundary layer of stagnant gases blankets the heating surface of coils externally thereof in a manner to create an insulating factor inasmuch as these boundary layers are extremely poor conductors of heat. By increasing the velocity of flow of gases about the coils, the boundary layers can be modified to thereby increase the quantity of heat which may be transmitted through the boundary layer. Thus, as the boundary layer thickness decreases, the rate of convection increases.